Master for barrier rib transfer mold, and method for forming barrier ribs of plasma display panel using the same

ABSTRACT

The invention relates to a method for forming barrier ribs of a plasma display panel. A master of barrier ribs for fabricating a mold for transferring barrier ribs is easily produced without the use of a machining technique. In the method for forming barrier ribs of a plasma display panel, a light-transmissive substrate having a predetermined pattern of a light-tight material formed on a surface and a photosensitive material layer bonded on the pattern is exposed to light from the rear surface of the light-transmissive substrate and developed so as to fabricate a master in which convex portions in a rib configuration are formed on the light-transmissive substrate. By using the master, a transfer mold for barrier ribs is fabricated. A rib material is filled in concave portions of the transfer mold and transferred onto a substrate for a PDP, thereby forming barrier ribs on the substrate for the PDP.

DESCRIPTION

1. Technical Field

The present invention relates to a master for fabricating a mold fortransferring barrier ribs and a method for forming barrier ribs of aplasma display panel (PDP) by using the same. More particularly, thepresent invention relates to a master for fabricating a mold fortransferring barrier ribs, the master having convex portions in abarrier rib configuration, and a method for forming barrier ribs of aplasma display panel (PDP) using the transfer mold fabricated with themaster.

2. Background Art

The PDP has been given attention as a display panel (low-profile displaydevice) which exhibits an excellent visibility, and its development hasbeen pursued to a high-definition display and a large screen display tofoster its versatility in the field of high-definition display in Japan.

The PDP is a display panel of a self-luminous type which has a dischargespace defined by a pair of substrates (typically, glass substrates)spaced a minute distance in an opposing relation with the peripherythereof being sealed.

In general, the PDP has partitions (also referred to as barrier ribs)having a height of about 100 μm to about 200 μm provided periodicallyfor partitioning the display space. For example, in a PDP of a surfacedischarge type suitable for fluorescent color display, barrier ribswhich are rectilinear as seen in a plan are equidistantly arranged alongdata electrode lines. The barrier ribs prevent the interference ofdischarge and the crosstalk of colors.

Various methods for forming barrier ribs have been proposed and carriedout. Typical examples include a screen printing method, a sand blastingmethod, an additive method (a lift-off method) and a photolithographicmethod.

The screen printing method is a method of forming barrier ribs bylaminating a glass paste on a substrate to a predetermined height byscreen printing, followed by firing.

The sand blast method is a method for forming barrier ribs by forming auniform barrier rib material layer on the entire surface of a substrate,forming a mask having a resistance to sandblast on desired portions ofthe substrate, thereafter, blowing an abrasive material thereon forcutting portions other than the mask, and after the completion ofcutting, removing the mask, followed by firing.

The additive method is referred to also as “embedding method” . First, apattern which is an image of barrier ribs is formed of a photosensitiveresist (typically, dry film) on desired sites of a substrate, and a ribmaterial is embedded in gaps between traces of the pattern by using ascreen printing method or the like. After the embedding of the ribmaterial, only the photosensitive resist pattern is stripped, andthrough firing, barrier ribs are formed.

The photolithographic method is a method for forming barrier ribs bycoating the entire surface of a substrate with a photosensitive ribpaste mixture of a photosensitive resin and a rib material, and exposingand developing a rib pattern. Hitherto, in this method, a thickness of afilm which can be exposed at a time is about 20 μm to about 30 μm, andtherefore exposure and development should be repeated several times toobtain barrier ribs with a desired height.

After the fabrication of a substrate by various methods as mentionedabove, the substrate is combined with an opposite substrate and theperiphery of the substrates is sealed with a sealing member. A dischargegas is filled in a panel, so that a PDP is completed.

As mentioned hereinabove, various methods have been proposed andperformed for the formation of barrier ribs. In any of the methods,however, a large percentage of cost is constituted by indirect materials(a dry film and a rib material to be disposed of) generated in thecourse of fabrication other than direct materials to form the barrierribs at a final stage and by consumable items (for example, printingpattern), which prevents the cost reduction.

As a measure for reducing the cost, consideration has been given to amethod of forming barrier ribs by transfer. In this method, a model ofbarrier ribs is produced and, using this model as a master, a mold forbarrier ribs is fabricated. Thereafter, a rib material is embedded inthe mold and transferred onto a substrate, thereby forming barrier ribs.

If the formation of barrier ribs is intended to be realized by aconventional molding technique, however, it is very difficult to patternby a machining technique a master for forming barrier ribs (width: 10μm-50 μm, height: 100 μm-200 μm, pitch: 100 μm-400 μm, area: 0.05 m²-0.5m², arrangement of barrier ribs: parallel or crossing arrangement, etc)required for fabrication of a low-profile display device such as a PDP.It is sometimes extremely difficult at the present level of thetechnique, depending on a configuration of side walls and an arrangementof the barrier ribs.

Under these circumstances, there has been a demand for a method ofeasily fabricating a master of barrier ribs for production of a mold ofbarrier ribs, without using the machining technique.

DISCLOSURE OF INVENTION

The inventors of the present invention have found that theaforementioned problem will readily be solved by fabricating a master ofbarrier ribs using a photosensitive material, producing a transfer mold(negative-type mold) using the master, and transferring a rib materialonto a substrate of a PDP with the mold or pressing the mold against therib material, thereby forming the barrier ribs.

Furthermore, the inventors have found that in the fabrication of themaster of barrier ribs, the utilization of rear-surface exposure andmulti-stage exposure ensures the control of a taper angle of the barrierribs (angle formed by the substrate surface and a barrier rib side face)and the adhesion of the photosensitive material to the substrate, sothat a master with a controlled configuration can be produced in anincreased yield and with ease.

Thus, the present invention provides a master for a barrier rib transfermold comprising: a light-transmissive substrate having a predeterminedpattern formed of a light-tight material on a surface of the substrateand having a photosensitive material layer formed on the pattern; andconvex portions in a desired pattern formed on the substrate by exposingthe substrate to light from a rear surface of the substrate, followed bydeveloping.

According to the present invention, a master to be used in a transfermethod (including a pressing method), which is an economical and simplemethod of forming barrier ribs, can easily be fabricated with a goodyield. Also, the control of the taper angle of barrier ribs and theformation of a pattern such as a lattice which have been extremelydifficult by machining processes can be achieved. In addition, thedesign of the pattern can readily be modified because the pattern isformed basically by photolithography.

Further, since the photosensitive material layer is exposed to lightfrom the rear surface of the substrate, photopolymerization progressesthe most in a contact site of the photosensitive material layer to thesubstrate. Thereafter, the adhesion between the substrate and thephotosensitive material is improved, compared to the case where theexposure is performed from the front surface of the substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a constitutional diagram of a plasma display according to thepresent invention;

FIG. 2 is a perspective view illustrating the internal construction of aPDP;

FIGS. 3(a) to (h) are explanatory views illustrating a first embodimentof a method of fabricating a master for formation of barrier ribs;

FIGS. 4(a) to (f) are explanatory views illustrating a second embodimentof a method of fabricating a master for production of barrier ribs;

FIGS. 5(a) to (f) are explanatory views illustrating a third embodimentof a method of fabricating a master for production of barrier ribs;

FIGS. 6(a) to (e) are explanatory views illustrating a fourth embodimentof a method of fabricating a master for production of barrier ribs;

FIG. 7 is an explanatory view illustrating a fifth embodiment of amethod of fabricating a master for production of barrier ribs;

FIGS. 8(a) to (c) are explanatory views illustrating a method oflaminating photosensitive material layers;

FIG. 9 is an explanatory view illustrating an example of theconfiguration of an end portion of a rib pattern formed of aphotosensitive material;

FIGS. 10(a) and (b) are explanatory views illustrating an example of theconfiguration of an end portion of a rib pattern formed of aphotosensitive material;

FIGS. 11(a) and (b) are explanatory views illustrating an example of theconfiguration of an end portion of a rib pattern formed of aphotosensitive material;

FIGS. 12(a) to (g) are explanatory views illustrating a method offabricating a master in which the property of transfer is improved;

FIG. 13 is an explanatory view illustrating a method of fabricating amaster in which the property of transfer is improved;

FIG. 14 is an explanatory view illustrating a method of fabricating amaster in which the property of transfer is improved.

BEST MODE FOR CARRYING OUT THE INVENTION

Usable as a light-transmissive substrate in the present invention is anysubstrate that is transmissive to exposure light, such as a glasssubstrate or a quartz substrate, for example. Usable as a light-tightmaterial is any material that is not transmissive to the exposure light,such as chromium oxide or various kinds of pigments. The formation ofthe predetermined pattern is achieved by a known method such as aspattering method using a mask.

A usable photosensitive material for the photosensitive material layeris not particularly limited and can be any known material. For example,a photosensitive material may be mentioned containing aphotopolymerizable compound (an acrylate, a methacrylate, urethanediacrylate, urethane dimethacrylate, etc.) having at least onepolymerizable unsaturated ethylene-like group in a molecule, aphotopolymerization initiator and a binder resin. The photosensitivematerial layer is formed by applying to the substrate a paste preparedby dissolution or dispersion of the above-mentioned photosensitivematerial in an appropriate solvent, or by laminating on the substratethe photosensitive material (typically referred to as a dry film resistor DFR in abbreviation) formed in advance into a sheet.

The photosensitive material can be exposed and developed by aconventionally known photolithographic technique. If the photosensitivematerial is of a negative type, for example, it is possible to form amaster for a barrier rib transfer mold having convex portions, forexample, in a rib configuration on the substrate by curing exposedportions by exposure and removing unexposed portions by development. Inthe exposure of the photosensitive material, it is important to performexposure from the rear surface of the substrate. In other words, thephotosensitive material is exposed in such a manner that light forexposure passes through the substrate. Part of the photosensitivematerial nearer to light is more photopolymerized and less susceptibleto a developer, so that a strong adhesion is obtained between thesubstrate and the photosensitive material. On the other hand, part ofthe photosensitive material more distant from light is notphotopolymerized so much because the light attenuates, and is moresusceptible to the developer so as to have a cured area smaller thanthat of the part nearer to the substrate. Thus, the resulting convexportions of the rib configuration are tapered to have a mountain-likeshape.

In the case where a DFR having the same thickness of a height of thebarrier ribs is not available, the photosensitive material layer may beformed of a plurality of photosensitive material layers. In this case,the photosensitive material layer may be formed of a plurality ofphotosensitive material layers different in sensitivity. For example, bylocating photosensitive material layers having weaker sensitivity inupper tiers, it is possible to produce a master with an increased taperangle owing to a multiplier effect of a light attenuation and thesensitivity properties possessed by the photosensitive materials. Thesensitivity of the photosensitive materials can be controlled by theselection of polymerization initiator and monomers and the dispersion ofpigments.

Further, a reflectance adjustment member may be disposed on thephotosensitive material layer to control the degree of exposure of adesired site of the photosensitive material layer during the exposureand adjust the configuration of the photosensitive material layer afterthe development.

By an alternative method, the convex portions can also be formed on thesubstrate by forming a first photosensitive material layer on a firstpattern previously formed of a light-tight material on a surface of thesubstrate, followed by exposure from the rear surface of the substrate;without development, forming a second photosensitive material layer onthe first photosensitive material layer; arranging a photolithographicmask having a second pattern overlying the first pattern on the secondphotosensitive material layer and exposing the second photosensitivematerial layer; repeating steps from the formation of the secondphotosensitive material layer a predetermined times; and developing allthe photosensitive material layers. This method enables theconfiguration of the side walls of the convex portions to be easilyadjusted in the design.

In this case, a translucent filter film may be formed for adjusting theamount of light during the exposure of the photosensitive materiallayers, on a region of the surface of the substrate where the firstpattern is not formed. Where the taper angle of the barrier rib isintended to be controlled, for example, a filter film having a pigmentdispersed therein may be formed on portions in which a reduced amount oflight for exposure is desired, so as to control the taper angle of thebarrier ribs. The filter film may have gradations such that it isthinner at the center of the barrier rib while it is thicker at edges ofthe barrier rib.

By a further alternative method, the convex portions may be formed onthe substrate by forming a first photosensitive material layer on afirst pattern of a light-tight material previously formed on the surfaceof the substrate; arranging a photolithographic mask having such asecond pattern that overlies the first pattern and allows a largerregion to be exposed than the first pattern on the first photosensitivematerial layer and exposing the first photosensitive material layer;without development, forming a second photosensitive material layer onthe first photosensitive material layer and exposing the secondphotosensitive material from the rear surface of the substrate; anddeveloping all the photosensitive material layers.

The present invention also provides a method for forming barrier ribs ofa plasma display panel, comprising: fabricating a mold for transferringbarrier ribs using the above-described master for the barrier ribtransfer mold, filling concave portions of the transfer mold with a ribmaterial, and transferring the rib material onto a substrate for theplasma display panel.

In the present invention, the master for the barrier rib transfer moldis used to fabricate the mold for transferring barrier ribs, and a ribmaterial is filled in the concave portions of the transfer mold andtransferred onto the substrate for the plasma display panel. Thetransfer mold can be fabricated by copying the master using a siliconerubber or the like. The transfer of the rib material onto the substratefor the plasma display panel can be carried out by embedding adielectric paste as the rib material in the concave portions of thetransfer mold of the silicone rubber and transferring the rib materialonto the substrate for the PDP itself, thereby forming the barrier ribson the substrate for the PDP. The transfer mold may be formed of a rigidresin or by way of electroforming, and may be used as a pressing mold tobe pressed against the dielectric rib material to obtain barrier ribs.

From the standpoint of a removal property during the transfer of the ribmaterial, it is desirable that the convex portions of the master for thebarrier rib transfer mold are configured such that end portions of thebarrier ribs have a larger area than main portions of the barrier ribwhen the rib material is transferred using the transfer mold.

Further, the master for the barrier rib transfer mold may be formed insuch a shape that its convex portions are formed of a plurality ofphotosensitive material layers in which a photosensitive material layersituated in an upper tier has a smaller area than a photosensitivematerial layer situated in a lower tier, so that when the barrier ribmaterial is transferred using the transfer mold, the end portions of thebarrier ribs in a longitudinal direction are lower than the mainportions of the barrier ribs.

Alternatively, the master for the barrier rib transfer mold may beformed in such a shape that its convex portions are formed of aplurality of photosensitive material layers in which a photosensitivematerial layer situated in an upper tier has a smaller area than aphotosensitive material layer situated in a lower tier and thephotosensitive material layer situated in the lower tier has a largerarea at sites corresponding to the end portions of the barrier ribs thanat sites corresponding to the main portions thereof, so that when thebarrier rib material is transferred using the transfer mold, the endportions of the barrier ribs has a larger area than the main portionsthereof and the end portions of the barrier ribs are lower than the mainportions thereof.

Further, the master for the barrier rib transfer mold may be formed insuch a shape that its convex portions are formed of a plurality ofphotosensitive material layers in which a photosensitive material layersituated in an upper tier has a smaller area than a photosensitivematerial layer situated in a lower tier and, in the photosensitivematerial situated in the lower tier, only the sites corresponding to theend portions of the barrier ribs are continuously connected, so thatwhen the barrier rib material is transferred using the transfer mold,the end portions of the barrier ribs are continuously connected and theend portions of the barrier ribs are lower than the main portionsthereof.

The present invention will now be explained in detail based onembodiments shown in the drawings. It should be understood that thepresent invention is not limited to the embodiments.

FIG. 1 is a constitutional diagram of a plasma display according to thepresent invention.

A plasma display 100 comprises an AC-driven PDP 1 as a color displaydevice employing a matrix display system and a drive unit 80 forselectively lighting cells C arranged lengthwise and crosswise whichconstitute a screen SC. The plasma display apparatus 100 is utilized aswall-mount TVs, monitors of computer systems, etc.

The PDP 1 is a three-electrode type surface discharge PDP in which pairsof sustain electrodes X and Y as first and second electrodes for maindischarge are arranged parallel to each other and orthogonal to addresselectrodes A as third electrodes. The sustain electrodes X and Y extendin a line direction (in a horizontal direction) in the screen. Thesustain electrodes Y are used as scan electrodes for selecting cells Cline by line during addressing. The address electrodes A extend in acolumn direction (in a perpendicular direction) and are used as dataelectrodes for selecting cells C column by column. The area where thegroup consisting of the sustain electrodes and the group consisting ofthe address electrodes intersect is a display area, i.e., the screen SC.

The driver unit 80 includes a controller 81, a frame memory 82, a dataprocessing circuit 83, a sub-field memory 84, a power source circuit 85,an X driver 87, a Y driver 88 and an address driver 89. Into the driverunit 80 is input field data Df for each pixel indicating luminous level(gradation level) of each color of R, G and B from an external devicesuch as a TV tuner or a computer, together with synchronous signals ofvarious types.

The field data Df is once stored in the frame memory 82, and then sentto the data processing circuit 83. The data processing circuit 83 is adata transforming means which divides one field into a predeterminednumber of sub-fields for gradation display, sets a combination ofsub-fields to be lit among the predetermined number of sub-fields andoutputs sub-field data Dsf corresponding to the field data Df. Thesub-field data Dsf is stored in the sub-field memory 84. The value ofeach bit of the sub-field data Dsf provides information indicatingwhether or not a cell needs to be lit in a sub-field, more specificallyrequirement or non-requirement of an address discharge.

The X driver 87 applies driving voltage to the sustain electrodes X andthe Y driver 88 applies driving voltage to the sustain electrodes Y. Theaddress driver 89 applies driving voltage to the address electrodes A inaccordance with the sub-field data Dsf. The power supply circuit 85supplies these drivers with a predetermined amount of power.

FIG. 2 is a perspective view illustrating the internal structure of thePDP.

In the PDP 1, a pair of sustain electrodes X and Y is provided on everyline L on an interior surface of a front glass substrate 11. Line L is arow of cells in the horizontal direction on the screen. The sustainelectrodes X and Y are each formed of a transparent conductive film 41of ITO and a metal film (bus conductor) 42 of Cr—Cu—Cr, and are coveredwith a dielectric layer 17 of low-melting point glass having a thicknessof about 30 μm. A protection film 18 of magnesium oxide (MgO) having athickness of angstroms of several thousands is provided on the surfaceof the dielectric film 17. The address electrodes A are arranged on anunderlying layer 22 which covers an interior surface of a rear glasssubstrate 21, and covered with a dielectric layer 24 having a thicknessof about 10 μm. Barrier ribs 29 each having a linearly elongateconfiguration in plan and a height of 15μm are provided between therespective address electrodes A. The barrier ribs 29 partition anelectric discharge space 30 on a subpixel-by-subpixel (unit luminousarea) basis in the line direction and define the height of the electricdischarge space 30. Three color (R, G and B) fluorescent layers 28R, 28Gand 28B for color display are respectively provided to cover interiorsurfaces of the rear substrate including surfaces above the addresselectrode A and side surfaces of the barrier ribs 29. The layout patternof three colors is a strip pattern in which cells in one column have thesame luminescent color and adjacent columns have different luminescentcolors. In the formation of the barrier ribs, it should be desirablethat top portions of thereof are colored dark and the other portionsthereof are colored white for improvement of reflectance of visiblelight, thereby enhancing contrast. The coloring of the barrier ribs iscarried out by adding a pigment of a predetermined color to a glasspaste serving as a material.

A discharge space 30 is filled with a discharge gas of a mixture ofxenon with neon as a main component (an enclosure pressure of 500 Torr),and the fluorescent layers 28R, 28G and 28B are locally excited byultraviolet light emitted from xenon during an electric discharge andemit light. Each pixel (picture element) for display is constituted bythree subpixels along the line L. A structural body within each subpixelis a cell (display element) C. The barrier ribs 29 are arranged in astripe pattern and, therefore, column sections of the discharge space 30corresponding to the respective columns are each continuous in thecolumn direction across all the lines. For this reason, aninter-electrode spacing between adjacent lines L (referred to as areverse slit) is selected to be a value (for example, a value within therange of 200 μm-500 μm) which is sufficiently larger than a surfacedischarge gap of each line L (for example, a value within the range of80 μm-140 μm) and prevent discharge coupling from generating in a columndirection. A light-tight film, not shown, is provided on either thefront surface or the rear surface of the substrate 11 for the purpose ofscreening a non-luminous whitish fluorescent layer of the reverse slit.

FIGS. 3(a)-(h) are explanatory views illustrating a first embodiment ofa method of fabricating a master for formation of barrier ribs.

In accordance with the method of forming barrier ribs of presentinvention, first, a master of barrier ribs is fabricated for productionof a mold for transferring barrier ribs.

In the fabrication of the master, a negative-type pattern of the barrierribs is formed of a light-tight material (for example, a thin chromiumfilm) 52 on a substrate 51 of glass (see FIG. 3(a)). The substrate 51may also be made of any other material that transmits light such asquartz or the like. The formation of the negative-type pattern ofbarrier ribs is carried out by spattering, for example.

On the pattern of the light-tight material 52, is formed a negative-typephotosensitive material (for example, a dry film resist, hereinafterreferred to as a DFR) 53 of which portions exposed to light is cured toremain (see FIG. 3(b)). In use of the DFR as the photosensitive material53, the DFR is laminated so that a substrate of a PDP will have barrierribs with a desired height since the DFR has a thickness of about 50 μmto about 100 μm.

Next, the substrate 51 is exposed from the rear surface thereof (seeFIG. 3(c)), and the photosensitive material 53 is exposed via thenegative-type pattern of the light-tight material 52 and developed (seeFIG. 3(d)). By doing this, photopolymerization progresses much at aportion of the photosensitive material 53 nearer to light, and thereforethe adhesion of the photosensitive material 53 to the substrate 51 isdrastically enhanced so that the stability in fabrication is ensured.Also, as applied light advances farther, it attenuates more, so that aportion intended to be a top portion of the barrier rib finally has avirtually lower degree of polymerization and therefore becomes narrowerduring development, thereby forming the barrier rib having anintentionally controlled taper. It is to be noted that since the controlof the taper of this type and the degree of stability in fabricationdepend on the required specs of the barrier ribs, the exposure from therear surface is not necessarily required and in some cases it ispossible to expose from the front surface.

The master of barrier ribs fabricated as described above is copied usinga silicone rubber or the like to form a transfer mold 54 (see FIG.3(e)), a dielectric paste 55 as a rib material is embedded in concaveportions of the mold 54 (see FIG. 3(f)) and transferred onto a substrate56 of the PDP itself (see FIG. 3(g)), thereby giving desired barrierribs 57 (see FIG. 3(h)).

Alternatively, the aforementioned mold 54 can be formed of a rigid resinor by electroforming, and pressed as a pressing mold against thedielectric rib material, so that desired barrier ribs are obtained. Itis to be noted that the substrate having the rib pattern formed of thephotosensitive material may be used as a master as it is or may be usedas an intermediate for repeated transfer with other resins or forproduction of a mold by electroforming.

It is to be noted that if an electrode pattern of the PDP (pattern ofthe address electrodes A shown in FIG. 2) per se is utilized as thenegative-type pattern of the light-tight material 52 and aphotosensitive rib material is used as the photosensitive material 53,it is possible to form barrier ribs self-aligned with the electrodes A(not requiring positioning) without using the transfer method.

Here, if the light attenuation rate of the photosensitive rib materialis the point at issue, the exposure may be performed at every formationof a photosensitive rib material layer, and all the photosensitivebarrier rib layers may subsequently be developed at once.

More specifically, first, the negative-type pattern of barrier ribs isformed on the substrate, and a first photosensitive rib material layeris formed thereon and exposed from the rear surface so that the adhesionof the first photosensitive rib material layer to the substrate isenhanced. Next, without development, a second photosensitive ribmaterial layer is formed on the first photosensitive rib material layer,and a negative-type pattern of the barrier ribs is formed thereon andthe second photosensitive rib material layer is exposed from the frontsurface thereof via the negative-type pattern. A third photosensitiverib material layer is formed on the second photosensitive rib materiallayer and exposed from the front surface thereof in the same manner. Theabove steps are repeated and all the photosensitive rib material layersare developed in order to form barrier ribs.

FIGS. 4(a) to (f) are explanatory views illustrating a second embodimentof a method of fabricating a master for production of barrier ribs.FIGS. 4(a), (c) and (e) are plan views, FIG. 4(b) is a side view of FIG.4(a), FIG. 4(d) is a side view of FIG. 4(c), and FIG. 4(f) is a sideview of FIG. 4(e).

In the present embodiment, to give positive control to the taper of thebarrier rib, the photosensitive material layer is formed by formingseveral layers so that, at every formation of a layer, exposure isperformed using an exposure pattern smaller than (pattern similar to)that used in the previous formation.

For example, the photosensitive material layer is formed of the threelayers by forming a first photosensitive material layer 53 a on thesubstrate 51; forming a negative-type pattern of barrier ribs thereonand exposing the substrate from the front surface (see FIGS. 4(a) and(b)) but not developing; forming a second photosensitive material layer53 b and exposing from the front surface thereof using a narrowerpattern than the previous pattern (see FIGS. 4(c) and (d)) but notdeveloping; next, forming a third photosensitive material layer 53 c,and exposing from the front surface thereof using a further narrowerpattern (see FIGS. 4(e) and (f)). It is to be noted that in the abovedescription the first photosensitive material layer 53 a is exposed fromthe front surface thereof but it is also possible that the negative-typepattern of the barrier ribs is formed in advance on the substrate 51 ofa light-transmissive material and the exposure from the rear surface iscarried out.

By developing all the photosensitive material layers which have beenexposed, the master with a tapered rib configuration can be formed.Steps caused by differences in width of the exposure patterns for therespective photosensitive material layers 53 a, 53 b and 53 c can bereduced to some extent by post-exposure baking (PEB).

From the master of the barrier ribs thus obtained, a transfer mold isfabricated in the same manner as in the first embodiment, and adielectric past as a rib material is embedded in concave portions of themold and transferred onto the substrate of the PDP so that desiredbarrier ribs can be obtained.

FIGS. 5(a) to (f) are explanatory views illustrating a third embodimentof a method of fabricating a master for production of barrier ribs.FIGS. 5(a), (c) and (e) are plan views, FIG. 5(b) is a side view of FIG.5(a), FIG. 5(d) is a side view of FIG. 5(c), and FIG. 5(f) is a sideview of FIG. 5(e). Each drawing illustrates the corresponding contentsshown in FIGS. 4 (a) to (f) as mentioned above.

In the present embodiment, in the formation of the negative-type ribpattern of the light-tight material 52 on the light-transmissivesubstrate 51, filter portions 52 a with a pigment dispersed are formedon portions in which attenuation of light is especially desired (in thepresent embodiment, portions corresponding to barrier ribs) while theother portions are covered with the usual light-tight material 52, sothat the taper angle of the barrier ribs is further controlled. Thefilter portions 52 a may have gradations such that the pigment is thinat the center of the barrier ribs while it is thick at the edgeportions. This filter has effect only at the exposure of from the rearsurface, and therefore it is more effective to use this filter incombination with the second embodiment.

The fabrication of the transfer mold using the master of barrier ribsand the transfer of the barrier ribs using the transfer mold are carriedout in the same manner as in the first and second embodiments.

FIGS. 6(a) to (e) are explanatory views illustrating a fourth embodimentof a method of fabricating a master for production of barrier ribs.

In the present embodiment, the taper angle of the barrier rib iscontrolled by using photosensitive materials different in thephotosensitivity. For example, on the substrate 51 having a pattern ofthe light-tight material 52 (see FIG. 6(a)), are formed a photosensitivematerial 53 d having a high sensitivity, a photosensitive material 53 ehaving an intermediate sensitivity and a photosensitive material 53 fhaving a low sensitivity in this order (see FIG. 6(b)), and exposed fromthe rear surface (see FIG. 6(c)) and developed (see FIG. 6(d)). Thisallows the effect of light attenuation and the sensitivity propertiesintrinsically possessed by the photosensitive materials 53 d, 53 e and53 f to produce the multiplier effect so that the master mold has alarge taper angle. It is to be noted that the sensitivity of thephotosensitive materials can be controlled by the selection ofpolymerization initiators, monomers and the like and the dispersion ofpigments.

The master of barrier ribs obtained as mentioned above is copied byusing a silicone rubber or the like in the same manner as in the firstto the third embodiment to fabricate a master mold 54 (see FIG. 6 (e)).A dielectric paste is embedded in the concave portions of the mastermold and transferred onto a substrate of the PDP to obtain desiredbarrier ribs.

Alternatively, as in the embodiment illustrated in FIGS. 3, the transfermold 54 can be formed of a rigid resin or by electroforming, and pressedas a pressing mold against the dielectric rib material, so that desiredbarrier ribs are obtained. In this case also, as mentioned above, thesubstrate having the rib pattern formed of the photosensitive materialmay be used as a master as it is or may be used as an intermediate forrepeated transfer with other resins or for production of a mold byelectroforming.

Incidentally, also in the present embodiment, as explained in theembodiment shown illustrated in FIG. 3, if an electrode pattern of thePDP per se is utilized as the negative-type pattern of the light-tightmaterial 52 and a photosensitive rib material is used as thephotosensitive material 53, it is possible to form barrier ribsself-aligned with the electrodes without using the transfer method.

FIG. 7 is an explanatory view illustrating a fifth embodiment of amethod of fabricating a master for production of barrier ribs.

The present embodiment can be applied to the first and fourthembodiments which use the rear-surface exposure. In the presentembodiment, in the exposure from a rear surface, a light absorbentmaterial 58 is disposed as a reflectance adjustment material on thephotosensitive material layer 53. In other words, a substance havingdesired reflectance is disposed on or applied to the photosensitivematerial layer 53, so that light reflectance is controlled in order toadjust the photopolymerization degree of a surface of the photosensitivematerial 53 and thereby control the pattern configuration. For example,if the light absorbent material 58 is black, it absorbs light and thepolymerization degree of the photosensitive material 53 is lowered toform a rib pattern with a narrow top, and if the light absorbentmaterial 58 is a substance scattering white color, halation is generatedand the polymerization degree of the photosensitive material 53 isenhanced to form a rib pattern with a wide top.

The fabrication of a transfer mold using the master of barrier ribs andthe transfer of barrier ribs using the transfer mold are carried out inthe same manner as in the first to fourth embodiment.

FIGS. 8(a) to (c) are explanatory views illustrating a method oflaminating photosensitive material layers.

The aforementioned formation methods of barrier ribs of the first to thefifth embodiment utilize at a final step a transfer method for theformation of barrier ribs. Accordingly, in these embodiments, theremoval property from the transfer mold is a fundamental point at issue.This removal property greatly depends on the taper angle of the barrierribs and the most important is the taper at the end portion of thepattern. Since transfer starts at the end portion of the pattern, it isbetter that the end portion has a larger taper and it is furtherpreferred that the end portion is so thin that the portion at which thetransfer starts is easily transferred.

Thus, at first, a first photosensitive material layer 53 a is formed onthe substrate 51 to have the same size as that of the substrate 51 andexposed (see FIG. 8(a)). Next, a second photosensitive layer 53 b isformed on the first photosensitive material layer 53 a to be shorter atboth ends in an extending direction of the barrier ribs and exposed (seeFIG. 8(b)). Then, a third photosensitive material layer 53 c is formedon the second photosensitive material layer 53 b to have the same sizeas that of the second photosensitive material layer 53 b and exposed(see FIG. 8(c)). That is, only the first photosensitive material layer53 a has a larger formation area, and the subsequently formed second andthird photosensitive material layers 53 b and 53 c each have a smallerformation area.

In this manner, it is possible to form a master having a shallow shapeonly at the end portion of the pattern by forming thin only thephotosensitive material at the end portion of the pattern so that theshape of the end portion of the pattern is shallow.

FIGS. 9, 10(a) and (b), and 11(a) and (b) are views illustratingexamples of the configuration of the end portion of the rib patternformed of the photosensitive material.

FIG. 9 also shows an example of a rib pattern in which the transferproperty is improved. As illustrated, if the end portion of the ribpattern formed of the photosensitive material 53 is wider than the mainportion of the rib pattern, the contact area is increased, resulting inimprovement of the transfer property.

FIGS. 10(a) and (b) illustrates an improved embodiment of FIG. 9, inwhich the end portions of the rib pattern are wider and lower than themain portions thereof. Such a master further improves the transferproperty.

A method of forming this master employs multi-stage exposure in which aplurality of photosensitive material layers are laminated and exposed aplurality of times for the formation of the photosensitive materiallayers 53 a, 53 b and 53 c with application of the laminating methodillustrated in FIG. 8.

For example, the photosensitive material layers are formed layer bylayer three times by forming a first photosensitive material layer 53 a;exposing it with a pattern in which intended feet of the barrier ribs,i.e., the main portions and end portions are wide (see FIG. 10(a));without development, forming a second photosensitive material layer 53 bthereon; superposing a pattern having no end portions thereon, followedby exposure but not development; forming a third photosensitive materiallayer 53 c thereon; and superposing a pattern narrower than the patternfor the second photosensitive material layer 53 b, followed by exposure(see FIG. 10(b)). After completion of exposure of all the photosensitivematerial layers, development is performed to give the master havingdesired barrier ribs.

FIGS. 11(a) and (b) illustrates a modified embodiment of FIGS. 10(a) and(b), in which the end portions of the rib pattern are connected. Thus,by variously combining the thickness and the number of thephotosensitive material layers, and the patterns for exposure, variousconfigurations of the end portions can be realized.

Further, it is possible to produce a master by, after the lowermostphotosensitive material layer is entirely exposed from the frontsurface, laminating another photosensitive material layer thereon, andexposing the photosensitive material layer from the rear surface via arib pattern, followed by developing, and to use the master for theformation of a transfer mold, thereby improving the transfer property.

That is, as illustrated in FIG. 12, first, a negative-type rib patternof the light-tight material 52 is formed on the glass substrate 51 (seeFIG. 12(a)), and a first DFR layer 59 is laminated thereon (see FIG.12(b)). Next, the DFR layer 59 is exposed via a photolithographic mask60 having a pattern for a foundation of an entire barrier rib surface(see FIG. 12(c)) but not developed. A DFR 61 constituted by three layersis laminated thereon (see FIG. 12(d)), exposed from the rear surface ofthe substrate via the pattern of the light-tight material 52 (see FIG.12(e)), and developed (see FIG. 12 (f)).

Thereafter, the master of barrier ribs thus obtained is copied by usinga silicone rubber or the like to fabricate a transfer mold 54 (see FIG.12(e)) and then fabricate a master configured as in FIG. 13. By usingthis master, the transfer property is further improved for the reasonsas follows.

That is, a transfer surface contacts the substrate by an areasubstantially equal to the area of the substrate and therefore thecontact area is the largest possible, which enhances the probability intransfer. Also, since the thickness of the foundation forming the bottomportion can be determined by the thickness of the first DFR layer, atransfer material has an improved uniform thickness at the bottomportion and can contact the substrate surely.

In order to further improve the release property in the convex portionsduring the transfer according to this method, the master may beconfigured as in FIG. 14. Further, the master may be formed such thatthe three-layered DFR 61 formed on the first DFR layer 59 is configuredas in FIG. 10 or 11.

As mentioned hereinabove, the present invention facilitates theproduction of a master for a barrier rib transfer mold a plasma displaypanel which has been extremely difficult by machining and the use of atransfer mold fabricated by employing the master enables the barrierribs of a plasma display panel to be formed accurately and easily.

What is claimed is:
 1. A master for a barrier rib transfer moldcomprising: a light-transmissive substrate having a predeterminedpattern formed of a light-tight material on a surface of the substrateand having a photosensitive material layer formed on the pattern; andconvex portions in a desired pattern formed on the substrate by exposingthe substrate to light from a rear surface of the substrate, followed bydeveloping.
 2. A master for a barrier rib transfer mold as set forth inclaim 1, wherein the photosensitive material layer comprises a pluralityof layers of photosensitive materials having different sensitivities. 3.A master for a barrier rib transfer mold as set forth in claim 1,wherein a reflectance adjustment member is disposed on thephotosensitive material layer to adjust a degree of exposure at adesired site of the photosensitive material layer during exposure.
 4. Amaster for a barrier rib transfer mold as set forth in claim 1, whereinthe photosensitive material layer comprises a plurality of layers, andthe convex portions are formed by forming a first photosensitivematerial layer on a first pattern of a light-tight material having beenformed beforehand on the surface of the substrate; exposing the firstphotosensitive material layer to light from the rear surface of thesubstrate; forming a second photosensitive material layer on the firstphotosensitive material layer as it is without being developed;disposing, on the second photosensitive material layer, aphotolithographic mask having a second pattern positionally overlapingthe first pattern and exposing the second photosensitive material layerto light; repeating steps after the formation of the secondphotosensitive material layer a predetermined number of times; andthereafter developing all photosensitive material layers.
 5. A masterfor a barrier rib transfer mold as set forth in claim 4, wherein atranslucent filter film is formed in a region of the surface of thesubstrate where the first pattern is not formed, for adjusting theamount of light during the exposure of the photosensitive materiallayers.
 6. A master for a barrier rib transfer mold as set forth inclaim 1, wherein the photosensitive material layer comprises a pluralityof layers, and the convex portions are formed by forming a firstphotosensitive material layer on a first pattern of a light-tightmaterial having been formed beforehand on the surface of the substrate;disposing, on the first photosensitive material layer, aphotolithographic mask having a second pattern which positionallyoverlaps the first pattern and which allows a larger region to beexposed than the first pattern and exposing the first photosensitivematerial layer to light; forming a second photosensitive material layeron the first photosensitive material layer as it is without beingdeveloped; exposing the second photosensitive material layer to lightfrom the rear surface of the substrate; and developing allphotosensitive material layers.
 7. A method of forming barrier ribs of aplasma display panel comprising: preparing a transfer mold for barrierribs using a master as set forth in claim 1; filling a barrier ribmaterial in concave portions of the transfer mold and transferring thebarrier rib material onto a substrate for a plasma display panel.
 8. Amethod of forming barrier ribs of a plasma display panel as set forth inclaim 7 characterized in that the convex portions of the master for abarrier rib transfer mold are formed in a shape such that, when thebarrier rib material is transferred using the transfer mold, endportions of barrier ribs have a larger area than main portions of thebarrier ribs.
 9. A method of forming barrier ribs of a plasma displaypanel as set forth in claim 7 characterized in that the master for abarrier rib transfer mold is formed in a shape such that its convexportions comprise a plurality of photosensitive material layers, thephotosensitive material layers are so formed that a photosensitivematerial layer situated in an upper tier has a smaller area than aphotosensitive material layer situated in a lower tier, and thereby,when the barrier rib material is transferred using the transfer mold,end portions of barrier ribs are lower than main portions of barrierribs.
 10. A method of forming barrier ribs of a plasma display panel asset forth in claim 7 characterized in that the master for a barrier ribtransfer mold is formed in a shape such that its convex portionscomprise a plurality of photosensitive material layers, thephotosensitive material layers are so formed that a photosensitivematerial layer situated in an upper tier has a smaller area than aphotosensitive material layer situated in a lower tier and thephotosensitive material layer situated in the lower tier has a largerarea in its sites corresponding to end portions of barrier ribs than inits sites corresponding to main portions of barrier ribs, and thereby,when the barrier rib material is transferred using the transfer mold,the end portions of the barrier ribs have a larger area than the mainportions of the barrier ribs and the end portions of the barrier ribsare lower than the main portions of the barrier ribs.
 11. A method offorming barrier ribs of a plasma display panel as set forth in claim 7characterized in that the master for a barrier rib transfer mold isformed in a shape such that its convex portions comprise a plurality ofphotosensitive material layers, the photosensitive material layers areso formed that a photosensitive material layer situated in an upper tierhas a smaller area than a photosensitive material layer situated in alower tier and, in the photosensitive material layer situated in thelower tier, only its sites corresponding to end portions of barrier ribsare continuously connected, and thereby, when the barrier rib materialis transferred using the transfer mold, only the end portions of thebarrier ribs are continuously connected and the end portions of thebarrier ribs are lower than main portions of the barrier ribs.